Free-flooded ring transducer with slow wave guide

ABSTRACT

This disclosure is directed to a free-flooded ring type transducer in combination with a coaxial slow waveguide for transmitting or receiving signals which improves the performance by delaying the radiation from the inner surface by one-half wavelength so that the radiation from the inner and outer surfaces are in phase.

Trott Aug; 28, 1973 FREE-FLOODED RING TRANSDUCER WITH 3,302,163 1/1967Andrews, Jr. 340/8 F1 SLOW WAVE GUIDE 2,922,140 1/1960 Levine et a1.340/8 FT 3,325,779 6/1967 Supemaw..... 340/8 FT n n r: infield J- T tt.An andale, Va. 3,142,034 7/1964 Junger 340/8 0 Assisnee: The Unitedstates of America as 3,243,766 3/1966 Wa1ther 340/8 FT represented bythe Secretary of the Navy, Washington, DC. Primary Examiner-.1. D.Miller Assistant Examiner-Mark O. Budd F [22] Apr 25 1972 AtI0rne v-R.S. Scrascra, Arthur L, Branmng et a1. [21] Appl. No.: 247,427

52 us. 01 310/8, 310/83, 310/90, [571 I ABSTRACT [51] l t Cl 310/26340/8 3 2 4: I This disclosure is directed to a free-flooded ring type nr transducer in combination with a coaxial Slow wave [58] Field ofSearch 310/82, 8.3, 8,

310/9 1 9 4 34mm 8 Fr 8 C guide for transmitting or receivingstgnalswhich |mproves the performance by delaying the radiation from 5 6R f C1 d the inner surface by one-half wavelength so that the ra- 1 eerences I e diation from the inner and outer surfaces are in phase.

UNITED STATES PATENTS 2,005,741 6/1935 Ha es 340/8 F1 2 Claims, 5Drawing Figures PAIENTEDMJBZB ms 3; 755.698

SHEU 2 (IF 3 RELATIVE SOUND PRESSURE LEVEL (dB) (:1 0 0| 6 G I I IPATENIEB M18 28 $75 ObN ObN

FREE-FLOODED RING TRANSDUCER WITH SLOW WAVE GUIDE BACKGROUND OF THEINVENTION This invention is directed to a free-flooded ring typetransducer and more particularly to an improved transducer.

Heretofore, free-flooded ring transducers in the form ofmagnetostrictive ring scrolls or piezoceramic rings have been used fordeep submergence sonar. array applications. Such arrays are affectedvery little by hydrostatic pressure, they are usually omnidirectional inthe plane of the ring and generally arrayed with more than one coaxialring. In order to obtain unidirection radiation the ring array must bethree-dimensional or mounted within a reflector.

It is well known that the acoustic radiation amplitude along the axis ofthe ring is quite low, relative to the radiation in the plane of thering. This is due to phase cancellation of the external and internalring radiation. At low frequencies, the ring transducer is equivalent totwo rings, the outer surface and the inner surface operating in phaseopposition. As the signal frequency increases, the radiation from theinner surface dominates due to the open-pipe resonance. Maximumefficiency occurs at the ring resonance and close coupling of the tworesonant frequencies provides a transducer which operates over a fairlybroad frequency range. An approximate mechanical circuit of amagnetostrictive ring has been set forth and explained in an articleApplication of a Slow Waveguide to a Free-Flooded Ring Transducer, by W.James Trott published in The Report of NRL Progress by the NavalResearch Laboratory dated May 1971.

SUMMARY OF THE INVENTION This invention is directed to arnagnctostrictive or piezoelectric ring type transducer which is coupledwith an axially aligned slow waveguide. The slow waveguide is made tojust fit inside of the inner diameter of the ring and yields maximumgain by delaying the radiation from the inner surface by one-halfwavelength so that the radiation from the inner and outer surfaces willbe in phase. As such, the structure provides a transducer which can beoperated at great depths with a unidirectional directivity with anincrease in source level (or directional gain). I

STATEMENT OF THE OBJECTS It is therefore an object of the presentinvention to provide a transducer structure which will operate at greatdepths with improved directional gain.

Another object is to provide a transducer structure by which the outputradiation from the inner and outer surfaces are in phase for onedirection along the axis of the ring.

Still another object is to provide a transducer which has an improvedunidirectional response.

Other objects and advantages of the invention will become obvious tothose skilled in the art upon reading the following description with areview of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the transducerarrangement with portions cut away for illustrative purposes.

FIG. 2 illustrates relative source level curves for the free-floodedring transducer with and without the slow waveguide.

FIGS. 3-5 illustrate comparative curves for the directional response atdifferent signal frequencies for the transducer with and without theslow waveguide.

DETAILED DESCRIPTION Now referring to the drawings, there is shown byillustration in FIG. 1 a free-flooded ring transducer made in accordancewith the teaching of the present invention. As shown, the transducerincludes a free-flooded ring 11 of piezoceramic or magnetostrictivematerial such as Permendur which is a cobalt-iron alloy of very highmagnetic saturation made by Allegheny Ludlum Steel Corporation. The ringhas a coil of wire 12 wound thereon which connects with a conductor 13through which a current is supplied from a suitable source. The entirestructure is coated with a protective coating 14 of hysol epoxy or anysuitable material to prevent harmful effects of sea water on themetallic elements and which will permit vibratory movement of the innerand outer surfaces of the ring element.

An elongated solid cylindrical element 15 made of silicone rubber havingan outer diameter substantially equal to the inner diameter of the ringstructure is secured in an axial relationship therewith. The elongatedcylindrical element may be inserted flush with the back face of thering, with the back end of the cylinder at the halfway point of thering, or with the back face of the cylinder flush with the front face ofthe ring in a coaxial arrangement. It has been determined that the bestre sults may be achieved with the front face of the ring flush with theback face of the silicone rubber cylinder as shown in FIG. 1.

The ring transducer is made of a 0.007 inch thick of 1.5 inch wide corewound about a mandrel into a scroll having an inside diameter of 5.63inches with an outside diameter of 6. l 3 inches. A bonding agent wasused between each layer to hold the scroll pennenently in shape. Thering was then wound with liner tape to insulate the ring from 210 turnsof No. 19 wire wound tightly upon the tape and connected to anelectrical lead. The resulting toroidally wound Permendur scroll corewas polarized by briefly passing Ampers of DC through the windings. Thewire wound core was then encapsulated in a clear HYSOL epoxy anorderless, tasteless, non-toxic, tough therrnosetting plastic that ishighly resistant to chemicals and has a high dielectric strength atradenarne of Houghton Laboratories Inc., Now HYSOL Corporation.

During encapsulation, a waxed wooden mold was fabricated to house thering core while the HYSOL epoxy was pouredaround it. The mold was placedin an oven and baked at 60C for 4 hours which is sufficient for theepoxy to harden. The mold was then removed and the encapsulatedtransducer was cleaned and sanded. The final product has an insidediameter of 5.3 inches an outside diameter of 6.53 inches and a width of1.90 inches.

The solid cylindrical silicone rubber has an outside diameter equal tothe inner diameter of the finished transducer element with a length of12% inches.

In operation the transducer assembly is placed in the water at thedesired depth. A signal is applied to the coil thereby causingvibrational movement of themagnetostrictive ring to produce soundpressure waves within the water. The waveguide is operative to delay thewave output of the inner surface of the ring by onestrictive ring aloneand the ring with the slow waveguide.

COMPARISON OF MEASURED PARAMETERS half wavelength. Thereby producing anoutput wave which is in phase with the wave produced by the outersurface. Thus, the transducer has unidirectional directivity withincreased source level.

FIG. 2 illustrates relative source level curves of the ring alone and ofthe ring in combination with the waveguide for relative sound pressurelevel (dB) vs Frequency kHz.

Curve 1 shows the axial far-field sound pressure for the combination,

Curve 2 shows the radial far-field sound pressure in the plane for thering for the combination,

Curve 3 is the back radiation of the combination,

Curve 4 shows the far-field axial sound pressure of the ring alone, and

Curve 5 shows the far-field radial sound pressure for the ring alone.The electrical current driving the ring is constant for these fivecurves. A significant improvement in source level is apparent bycomparison of cures 1 and 5.

FIGS. 3, 4, and 5 illustrate a comparison of directional response forthe free-flooded ring alone and the free-flooded ring in combinationwith the slow waveguide at 6kHz, 7kHz and 8kHz, respectively. Thefreeflooded ring alone is shown on the right side, and the combinationon the left side. The dashed curves in FIG. 3 is a Sinl) directivitypattern at frequencies below the resonant frequencies which is seen tobe substantially that of the 6kHz pattern which is above the open piperesonance. In three dimensions the directivity is a figure of revolutionabout the 0 axis.

The following table illustrates a comparison of different measuredparameters for the free-flooded magneto- Comparing the correspondingmeasurements at the respective frequencies, illustrates an increase inefficiency for each of the frequencies where the transducer included theslow waveguide. Further, one concludes that the application of a slowwaveguide to a free flooded ring transducer yields a significantimprovement in directivity and source level.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

l. A free-flooded ring transducer which includes:

a transducer ring element,

means connected with said ring element for applying a signal sourcethereto to produce vibrational movement in said ring element, and

a slow waveguide operatively connected with said ring element in axialalignment therewith,

said slow waveguide is made of silicone rubber of cylindrical shape,

whereby sound pressure radiation from the inner surface of said ring isdelayed by one-half wavelength so that the sound wave radiation from theinner and outer surfaces are in phase in one direction along the ringaxis.

2. A free-flooded ring transducer as claimed in claim 1; wherein,

said slow waveguide has an outer diameter substantially equal to theinside diameter of said ring element and is coaxial therewith.

1. A free-flooded ring transducer which includes: a transducer ringelement, means connected with said ring element for applying a signalsource thereto to produce vibrational movement in said ring element, anda slow waveguide operatively connected with said ring element in axialalignment therewith, said slow waveguide is made of silicone rubber ofcylindrical shape, whereby sound pressure radiation from the innersurface of said ring is delayed by one-half wavelength so that the soundwave radiation from the inner and outer surfaces are in phase in onedirection along the ring axis.
 2. A free-flooded ring transducer asclaimed in claim 1; wherein, said slow waveguide has an outer diametersubstantially equal to the inside diameter of said ring element and iscoaxial therewith.